BackgroundSelenium (Se) is an essential trace element in living systems. Microorganisms play a pivotal role in the selenium cycle both in life and in environment. Different bacterial strains are able to reduce Se(IV) (selenite) and (or) Se(VI) (selenate) to less toxic Se(0) with the formation of Se nanoparticles (SeNPs). The biogenic SeNPs have exhibited promising application prospects in medicine, biosensors and environmental remediation. These microorganisms might be explored as potential biofactories for synthesis of metal(loid) nanoparticles.ResultsA strictly aerobic, branched actinomycete strain, ES2-5, was isolated from a selenium mining soil in southwest China, identified as Streptomyces sp. based on 16S rRNA gene sequence, physiologic and morphologic characteristics. Both SEM and TEM-EDX analysis showed that Se(IV) was reduced to Se(0) with the formation of SeNPs as a linear chain in the cytoplasm. The sizes of the SeNPs were in the range of 50–500 nm. The cellular concentration of glutathione per biomass decreased along with Se(IV) reduction, and no SeNPs were observed in different sub-cellular fractions in presence of NADPH or NADH as an electron donor, indicating glutathione is most possibly involved in vivo Se(IV) reduction. Strain ES2-5 was resistant to some heavy metal(loid)s such as Se(IV), Cr(VI) and Zn(II) with minimal inhibitory concentration of 50, 80 and 1.5 mM, respectively.ConclusionsThe reducing mechanism of Se(IV) to elemental SeNPs under aerobic condition was investigated in a filamentous strain of Streptomyces. Se(IV) reduction is mediated by glutathione and then SeNPs synthesis happens inside of the cells. The SeNPs are released via hypha lysis or fragmentation. It would be very useful in Se bioremediation if Streptomyces sp. ES2-5 is applied to the contaminated site because of its ability of spore reproduction, Se(IV) reduction, and adaptation in soil.

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A Gram-stain-negative, non-motile, rod-shaped, aerobic bacterium, designated strain YLT18 T , was isolated from mountain cliff soil of Enshi Grand Canyon in China. The major menaquinone was menaquinone 7 (MK-7) and the predominant fatty acids (.5 %) were iso-C 15 : 0 , C 16 : 1 v5c, iso-C 17 : 0 3-OH, summed feature 3 (C 16 : 1 v7c/iso-C 15 : 0 2-OH) and iso-C 15 : 0 3-OH. The major polar lipids were phosphatidylethanolamine, two unknown aminophospholipids, two unknown aminolipids and two unknown polar lipids. T showed obvious differences from the closely related species in terms of esterase (C4) activity, acid production from fructose and rhamnose, and sole carbon source utilization by arabinose and rhamnose. The results from this polyphasic taxonomic study revealed that strain YLT18 T represents a novel species of the genus Chitinophaga, for which the name Chitinophaga barathri sp. nov. is proposed. The type strain is YLT18 T (5KCTC 42472 T 5CCTCC AB 2015054 T ).

A novel Gram-stain-negative, strictly aerobic, non-motile, rod-shaped, capsule-forming bacterium, designated strain YLT33T, that formed orange-red colonies was isolated from mountain cliff soil from Enshi Grand Canyon, southwest China. Growth occurred at 4-35 °C (optimum 28 °C) and at pH 6.0-10.0 (optimum 7.0). It showed maximum (99.3 %) 16S rRNA gene sequence similarity and formed a monophyletic clade with Sphingoaurantiacus polygranulatusMC 3718T (=CCTCC 2014274T). The DNA G+C content was 68.5 mol% and strain YLT33T showed a 50.5 % DNA-DNA relatedness value to S. polygranulatusMC 3718T. The major fatty acids (>5 %) were C17 : 1ω6c (40.7 %), C15 : 0 (10.4 %), C15 : 1ω6c (9.4 %), summed feature 3 (C16 : 1ω7c and/or iso-C15 : 0 2-OH; 8.6 %), C17 : 1ω8c (7.1 %), C18 : 1ω7c (6.1 %), and C15 : 0 2-OH (5.7 %). Ubiquinone-10 was the sole respiratory quinone. The polar lipids of strain YLT33T contained diphosphatidylglycerol, phosphatidylglycerol, phosphatidylethanolamine, phosphatidylcholine, sphingoglycolipid, two unknown glycolipids and one unknown phospholipid. Carotenoids were present in cells. Homospermidine was the major polyamine. In addition, strain YLT33T showed obvious differences from the closely related strain S. polygranulatusMC 3718T with respect to major polar lipids, fatty acids and other morphological, physiological and biochemical characteristics. These results from polyphasic taxonomic studies reveal that strain YLT33T represents a novel species of the genus Sphingoaurantiacus, for which the name Sphingoaurantiacuscapsulatus sp. nov. is proposed. The type strain is YLT33T (=CCTCC AB 2015150T=KCTC 42644T).

A Gram-stain-negative, light pink, non-motile, rod-shaped, aerobic bacterium, designated strain XNV015T, was isolated from soil of a vanadium mine. Phylogenetic analyses based on 16S rRNA gene sequences indicated that it belongs to the genus Pedobacter and was closely related to Pedobacter suwonensis DSM 18130T (96.93 % sequence similarity), Pedobacter alluvionis NWER-II11T (96.66 %), Pedobacter terrae DS-57T (96.54 %), Pedobacter kyungheensis KACC 16221T (96.54 %) and Pedobacter soli KACC 14939T (96.47 %). This strain clearly differed from the closely related species in terms of acid production from rhamnose and ethanol. Menaquinone-7 was the predominant respiratory quinone. The predominant fatty acids included iso-C15 : 0, C16 : 1ω5c, summed feature 3, iso-C17 : 0 3-OH and C17 : 0 2-OH. The major polar lipids were phosphatidylethanolamine, glycolipids, lipids and aminolipids. The genomic DNA G+C content was 43.8 mol%. The genotypic analysis, biochemical properties, and phenotypic and chemotaxonomic characteristics indicate that strain XNV015T represents a novel species of the genus Pedobacter, for which the name Pedobacter vanadiisoli sp. nov. is proposed. The type strain is XNV015T (=CCTCC AB 2015319T=KCTC 42866T).